How can i fill a hole in this mesh
First off, its hard to tell from the picture but the last edge loop looks very thick, possibly indicating there is a double edge there? maybe check that but otherwise, i made a cylinder with the same amount of edges, the extra extruded edges and triangles. The grid fill seems to work fine if you have the right settings and right active edge.

Or am I missing somthing? is this not the desired effect?